Simulations

Figure 2. Results comparison between 0D numerical simulations and measured operating parameters obtained during an experimental investigation of four-stroke diesel engine

0D (Zero-Dimensional) simulations

0D (zero-dimensional) simulation models assumes a homogeneous mixture of gases in any internal combustion engine cylinder. Such simulations are extremely fast, they allow accurate and precise tracking of operating parameters for the entire internal combustion engine, but the details inside each engine cylinder cannot be tracked. Figure 1 presents combustion space inside one internal combustion engine cylinder which is used as a baseline for defining equations for this simulation model. Figure 2 presents results comparison between 0D numerical simulations and measured operating parameters obtained during an experimental investigation of four-stroke diesel engine.

Figure 1. Combustion volume of one cylinder with system borders – 0D numerical model

QD (Quasi-Dimensional) simulations

Quasi-Dimensional (QD) numerical simulations divides each fuel spray on independent control volumes, Figure 3. Each control volume of each fuel spray is observed independently, for each control volume are calculated mass and energy balances, as well as chemical reactions. In those numerical models is assumed that between fuel spray control volumes did not exist any interaction. The only allowed interaction is between fuel spray control volumes and ZWC (Zone Without Combustion) by air inflow into each control volume of each fuel spray in order to allow fuel evaporation, mixture preparation and combustion.

Such simulations require more computational resources in comparison to 0D simulations, calculation time is higher, but QD simulations allow a detail analysis of processes inside internal combustion engine cylinder. Figure 4 presents final result of QD simulation by direct comparison of cylinder pressure change with measured values obtained in the laboratory.

Figure 3. Division of each fuel spray into the control volumes in QD numerical simulation

Figure 4. Comparison of cylinder pressure change obtained by QD numerical simulation and measured in the laboratory

Figure 5. Temperature fields for different water injection locations, crank angle (CA) = 15°. (a) same location of the water and fuel nozzle; (b) water nozzle over the fuel nozzle; (c) water nozzle under the fuel nozzle; (d) case with a water nozzle over and under the fuel nozzle

Figure 6. Local nitrogen-monoxide (NO) concentration for different water injection locations, crank angle (CA) = 15°. (a) same location of the water and fuel nozzle; (b) water nozzle over the fuel nozzle; (c) water nozzle under the fuel nozzle; (d) case with a water nozzle over and under the fuel nozzle

Figure 7. Nitrogen-monoxide (NO) mass fractions inside diesel engine cylinder for various EGR (Exhaust Gas Recirculation) rates

CFD simulations

CFD (Computational Fluid Dynamics) simulations allow detail tracking of processes inside internal combustion engine cylinders and very precise simulation in relation to real processes. In such simulations, the whole space inside cylinder is divided on the control volumes and for each control volume are calculated mass and energy balances, as well as chemical reactions. From the computational resources viewpoint, these simulations are the most complex and it requires much higher simulation time in comparison to 0D and QD simulations.

Figure 5 presented temperature fields inside marine two-stroke diesel engine cylinder during the simulation of different water injection locations. The water injection process enables a significant decrease of maximum temperatures inside the cylinder and consequentially decreases nitrogen-oxides (NOx) emissions. Figure 6 presents local concentrations of the nitrogen-monoxide (NO) inside the marine two-stroke diesel engine cylinder during the analysis of different water injection techniques.

Figure 7 presents a CFD simulation of nitrogen-monoxide (NO) mass fractions change in the diesel engine cylinder for different EGR (Exhaust Gas Recirculation) rates. From Figure 7 is obvious that nitrogen-monoxide mass fractions and concentrations decreases with higher EGR rate.

Numerical simulations by using AI methods

The usage of Artificial Intelligence (AI) methods allows the internal combustion engine process analysis and prediction of engine operating parameters. Figure 8 presents the change in specific fuel consumption, while Figure 9 presents the change in maximum cylinder pressure for marine two-stroke diesel engine during the variations in SOI (Start Of Injection) and during simultaneous variations in EVO (Exhaust Valve Opening). Figure 8 and Figure 9 are obtained as a numerical simulation result for marine two-stroke diesel engine by using MLP (Multi-Layer Perceptron) neural networks.

Figure 8. Specific fuel consumption be (g/kWh) at full load of marine two-stroke diesel engine during the variations in SOI (Start Of Injection) and during simultaneous variations in EVO (Exhaust Valve Opening)

Figure 9. Maximum cylinder pressure pmax (MPa) at full load of marine two-stroke diesel engine during the variations in SOI (Start Of Injection) and during simultaneous variations in EVO (Exhaust Valve Opening)

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